1. Field of the Invention
The present invention relates to H-driver modules and more particularly, in a preferred embodiment to H-drivers for driving air-core magnetic gauges.
2. Description of the Prior Art
An air-core gauge normally has a rotor with a magnetic sensitive region disposed perpendicular to an indicating dial shaft and a pair of stator windings; i.e., a COSINE or vertical (V) winding and a SINE or horizontal (H) winding fixedly arranged at right angles about the shaft. The gauge has a dial and a dial needle that moves over quadrants of the dial in response to movement of the rotor.
Prior art dual half-bridge push-pull drivers (H-drivers) control the operation of the air-core gauge in response to a pair of modulated pulse width streams (PWM) and four control logic current direction signals (DIRs) to provide a resultant magnetic field for rotating the rotor. The DIR signals select the direction that current passes through the windings of each half of the bridge to place the needle in each of four quadrants of the dial. The PWM signals, a first and a second positive pulse signal, control the direction and amount the needle moves over the dial within the selected quadrant by causing changes in magnitude of the current passing through each winding.
Modulation of the current in the horizontal and vertical windings respectively vary from 0 to 100% in proportion to related variations of SINE and COSINE wave functions values between 0.degree. and 90.degree. which defines the angular position of the needle on the dial. Current in each winding varies in relation with the ON time duration of the modulated pulse stream to produce resultant magnetomotive force (mmf) vectors; the needle position varying in respect to the vector sum of the SINE and COSINE waves that represent the equivalent % on time the PWM signal.
Illustratively, when a PWM signal applied to a H-winding stays ON 20% of the time, the PWM signal on a V-winding stays ON approximately 97.5% of the time during the same cycle; the current and magnetic field in the V-winding increases while the current and magnetic field of the H-winding decreases causing the rotor to rotate until magnetic quiescence results between the two fields and the magnetic sensitive region of the rotor, deflecting the needle to locate at about 11.25.degree. on the dial. 11.25.degree. corresponds to the vector sum of the COSINE and SINE functions when a 20% duration first PWM signal is applied to the H-winding while 971/2% duration second PWM signal is applied to the V-winding.
If the % ON time of the PWM signal on the H-winding changes to 97.5% while the % ON time of the PWM signal on the V-winding changes to 20%, the needle seeks a location of about 78.75.degree. on the dial. Of course, if the % ON time of the two pulse streams change back to the original 20:97.5% or greater, then the quiescent effect of the fields cause the needle to rotate backwards towards the original 11.25.degree. location on the dial.
A problem occurs in the prior art push-pull type H-drivers when an attempt to move the needle from, e.g., a 6.4.degree. position to 0.degree. on the dial, or from 83.degree. to 90.degree. on the dial or vice-versa. The needle tends to stick. In these regions of the dial, the % ON time of the pulses have ratios of 5:99.5% or lesser. At these ratios, the magnetic field in the dominant winding appears to swamp or dwarf any effect of the magnetic field of the recessive winding. Hence a quiescent result occurs that seems to bound the magnetic region of the rotor to the dominant field rather than to both fields.
Realizing the needle sticking problem of the push-pull H-driver/air-core gauge circuits, a search for other circuits and schemes to eliminate the problem was initiated. This search resulted in the improved device of the present invention.